Method and device for supplying information, an alert or alarm for an aircraft in proximity to the ground

ABSTRACT

Information, an alert or an alarm is supplied to an aircraft in proximity to the ground. A grid of geographic coordinates is established, each mesh of which exhibits a defined relief. The trajectory of the aircraft is predicted over a predetermined time interval. An intersection, if any, between the predicted trajectory and the relief of at least one of the meshes is determined. An alert or alarm is activated in the case of such an intersection. The alert or alarm is inhibited when the aircraft is in landing configuration or when the runway is detected and a series of conditions relating to landing are fulfilled.

FIELD OF THE INVENTION

The present invention relates to a method and a device for supplyinginformation, an alert or alarm for an aircraft maneuvering above terrainwith known relief, particularly in the vicinity of a runway for theaircraft, when the trajectory of the aircraft is capable of interceptinga relief of said terrain.

DESCRIPTION OF RELATED ART

It has proved to be necessary, for aircraft in flight, to provide analarm system making it possible, in good time, to detect and signalproximity of the relief (in a general way, of the ground), which is adanger to the aircraft. A currently widespread system is GPWS, standingfor "Ground Proximity Warning System". GPWS uses the radio altimetermeasurement of the height of the aircraft above the ground situated inthe vertical to its instantaneous position. The comparison of theseradio-altimeter data and the vertical speed parameters, among others(pitot-static vertical speed and radio altimeter rate of approach to theground), with respect to various predetermined thresholds, allowsvarious types of visual and audible alarms to be triggered. Alarms makeit possible to warn the pilot of a dangerous situation risking acollision with the ground in the near future if no corrective action istaken on the controls making it possible rapidly to regain sufficientaltitude to guarantee the safety of the aircraft. The main drawback ofthis system lies in the high number of false alarms which it generates.

Another system of this type is also known, but based on a differentprinciple from that used by GPWS, to evaluate the level of danger whichthe ground represents for the aircraft. In this case, the measuredposition of the aircraft in the horizontal and vertical planes is usedso as to calculate a prediction of the changes in the various possibletrajectories of the aircraft in the moments which follow themeasurement, and to compare the envelope of these trajectories with thesafety altitudes described in a ground-related database, calculated,particularly, from the various heights of the surface of the groundoverflown by the predicted trajectories.

The detection of an intersection between the envelope of trajectoriesand the safety volume defined by the ground-related database makes itpossible to predict that the aircraft risks departing from the range ofsafety altitudes in a time interval which is determined in advance. Analert or alarm can then be generated so as to warn the pilot of thisdanger situation so that he returns to an acceptable safety altitude asrapidly as possible.

In this system, the ground (terrain)-related database consists of therecording of safety altitudes corresponding to each of the meshes of thegrid describing the terrain. The grid defines subdivisions of thesurface of the earth which, for example, may be referenced in geographiccoordinates. The grid then consists of a network of adjacent meshes.Each mesh has a safety altitude attributed to it, guaranteeing thatoverflying this mesh, at least at this altitude, will entail nocollision with the terrain described in this mesh. The main drawback ofthis system lies in the short timescale left to the crew to react tocertain rapid variations in the relief which are associated with anumber, which may be high, of false alarms which they generate.

The alarm is generated based on the detection of a "conflict"(interception) between the trajectory of the aircraft and the relief ofan element (mesh) of the ground- or terrain-related database.

The position (in terms of Ox, Oy and Oz coordinates) of the aircraft isextrapolated for an all-inclusive maximum anticipation time of the orderof one minute or less (for example 30 or 60 seconds) along the directionof the ground speed vector (speed with respect to the ground).

This timescale has been chosen inclusively in order to include thefollowing reaction times:

sensor reaction time;

alarm algorithm calculating time;

crew reaction time; this time depends on the phase of flight, sincevigilance is variable in the course of a flight;

reaction time between the pilot's command and the movement of thecontrol surfaces;

time characteristic of the minimum performance of the aircraft,depending on configuration (gears, flaps, engine failure, particularly);

time related to margins with respect to the terrain.

Prediction of the aircraft's trajectory is obtained by calculating thetrajectory prediction segment in three dimensions. This means a linearextrapolation along the ground speed vector of the aircraft, that is tosay making a tangent to the trajectory. Thereafter, the elements of therelief which the aircraft is likely to overfly during the extrapolationtime are determined. For each mesh of the grid overflown, the predictedaltitude of the aircraft at entry and exit to and from the mesh arecalculated, using the vertical speed Vz of the aircraft. When theextrapolated trajectory segment of the aircraft intercepts a mesh of theterrain grid while having a predicted altitude less than the altitude ofthe region in question, the alarm is triggered.

Inevitably, there comes a moment in the trajectory prediction when theprediction segment intercepts the ground, during the landing phase,before touchdown. This alarm is known as a nuisance alarm, since itoccurs while the aircraft is in the normal flight situation, the pilotstarting the landing.

This signal is troublesome to the pilot, since he is accustomed toreacting quickly and in a certain way. However, if the treatment of analarm is not unique and introduces confusion as to the type of safetyaction to be undertaken (in this case, an absence of action), theeffectiveness of the corrective action will consequently be reduced,being less rapid.

SUMMARY OF THE INVENTION

The object of the present invention is to avoid this drawback.

To this end, the method for supplying information, an alert or alarm foran aircraft manoeuvering above terrain with known relief, especially inthe vicinity of a runway for said aircraft, when the trajectory of theaircraft is capable of intercepting a relief of said terrain, in which:

for said terrain, a grid of geographic coordinates is established, eachmesh of which has a defined relief,

the trajectory of the aircraft, over a predetermined time interval, ispredicted,

any intersection between said trajectory and the relief of at least oneof said meshes is determined, and

an alert or alarm is triggered depending on the result of saiddetermination,

is noteworthy, according to the invention, in that a comparison isperformed between the meshes of the grid which are intercepted by saidpredicted trajectory and the meshes containing the runway for theaircraft, so that, if the information supplied by said comparison isnegative, the alert or alarm remains capable of being activated, and thealert or alarm is inhibited if the information supplied by saidcomparison is positive and if, moreover, the following conditions aresimultaneously fulfilled:

the ground speed of the aircraft is less than or equal to apredetermined threshold,

the altitude of the aircraft above the ground is less than or equal to apredetermined threshold,

the aircraft is at least substantially in the axis of the runway, and

the aerodynamic configuration of the aircraft corresponds to the landingphase thereof.

Hence, criteria are defined making it possible to detect that theaircraft's approach to the ground is performed in an approach zone of arunway, while, at the same time, the normal landing conditions arefulfilled. Moreover, inhibition of the alert or alarm occurs asufficient time in advance, equal at most to the time interval chosen(for example, 30 seconds) for the trajectory prediction.

Advantageously, for given terrain, in the vicinity of one or morerunways contained in this terrain, a grid is established with finermeshing than anywhere else.

Preferably, as conditions of aerodynamic configuration of the aircraftwhich are associated with the landing phase, account is taken of thefollowing criteria: slats and flaps extended, and landing gear lowered.

The present invention also relates to a device for supplyinginformation, an alert or alarm, for implementing the method above, foran aircraft manoeuvering above terrain with known relief, particularlyin the vicinity of a runway for said aircraft, when the trajectory ofthe aircraft is capable of intercepting a relief of said terrain,comprising:

means of establishing a grid of geographic coordinates, for saidterrain, each mesh of which exhibits a defined relief,

means of predicting the trajectory of the aircraft over a predeterminedtime interval,

means of determining any intersection between said predicted trajectoryand the relief of at least one of said meshes, and

alert or alarm means which are capable of being activated subject tosaid determination means,

noteworthy in that it includes, between said determination means andsaid alert or alarm means, means for comparison between the meshes ofsaid grid which are intercepted by said predicted trajectory and themeshes containing the runway for the aircraft, such that, if theinformation supplied by said comparison means is negative, said alert oralarm means remain capable of being activated, and said alert or alarmmeans are inhibited if the information supplied by said comparison meansis positive and if, moreover, the following conditions aresimultaneously fulfilled:

the ground speed of the aircraft is less than or equal to apredetermined threshold,

the altitude of the aircraft above the ground is less than or equal to apredetermined threshold,

the aircraft is at least substantially in the axis of the runway, and

the aerodynamic configuration of the aircraft corresponds to the landingphase thereof.

Advantageously, between said comparison means and said alert or alarmmeans, a logic element, such as an AND gate is provided, the inputs ofwhich receive the information supplied by said comparison means when itis positive and the conditions relating to the situation and to theconfiguration of the aircraft, and the output of which is linked to saidalert or alarm means.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures of the attached drawing will give a good understanding ofhow the invention can be produced.

FIG. 1 is a block diagram of the device according to the invention.

FIG. 2 shows a grid of geographic coordinates, certain meshes of which,with defined relief, are traversed by a segment of predicted trajectoryof an aircraft.

FIGS. 3 and 4, relating to the grid of FIG. 2, illustrate in elevation,respectively, the case where said predicted trajectory segment does anddoes not intercept the relief of a mesh of said trajectory.

FIG. 5 shows a grid similar to that of FIG. 2 in the vicinity of arunway for the aircraft.

FIG. 6 is a view in elevation of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With regard to FIG. 1, the device 1 for supplying information, an alertor alarm for an aircraft manoeuvering above terrain with known relief,particularly in the vicinity of a runway for said aircraft, when thetrajectory of the aircraft is likely to intercept a relief of saidterrain, comprises:

means 2 of establishing a grid of geographic coordinates for saidterrain, each mesh of which exhibits a defined relief,

means 3 of predicting the trajectory of the aircraft over apredetermined time interval,

means 4 of determining any intersection between said predictedtrajectory and the relief of at least one of said meshes, saiddetermination means 4 being linked to said means 2 of establishing thegrid and to said trajectory prediction means 3 by respective links 5 and6,

alert or alarm means 7 capable of being activated subject to saiddetermination means 4 to which they are linked by a link 8.

More precisely, the trajectory of the aircraft can be predicted, over apredetermined time interval, by inputting, into the prediction means 3,the information relating to the position of the aircraft at the initialinstant: latitude 9, longitude 10, altitude 11; at the time interval 12in question; and at the ground speed 13 of the aircraft.

FIG. 2 shows a grid G of geographic coordinates LA, LO, certain meshes Mof which, of defined relief R (as can be seen in FIGS. 3 and 4), aretraversed by a segment of predicted trajectory T of the aircraft A, froma position Po to a position Pt. As indicated above, a simple trajectoryprediction model can be used, considering the extrapolation of theground speed vector of the aircraft over a predetermined extrapolationtime t, equal, for example, to 30 seconds.

According to the trajectory segment thus predicted and the relief of themeshes traversed, it is possible to predict whether (FIG. 4) or not(FIG. 3) a risk exists that the predicted trajectory T of the aircraft Aintercepts the relief of a mesh, and to do so sufficiently in advance inorder to be able to remedy it in time, by virtue of the alert or alarmtriggered at this moment.

However, as illustrated in FIGS. 5 and 6, this mode of operationinevitably entails the predicted trajectory T of the aircraft A"meeting" the ground, in the vicinity of a runway B, thus triggering aninadvertent alert or alarm.

In order to overcome this drawback, the device 1 according to theinvention includes (FIG. 1), between the determination means 4 and thealert or alarm means 7, means 14 for comparison between the meshes ofthe grid G which are intercepted by the predicted trajectory T and themeshes containing the runway B for the aircraft A, such that, if theinformation supplied by the comparison means 14 (linked by the link 15to the means 2 for establishing the grid) is negative (absence of"intersection" with the meshes of the runway), the alert or alarm means7 remain capable of being activated, whereas they are inhibited if theinformation supplied by the comparison means 14 is positive (existenceof an "intersection" with the meshes of the runway) and if, moreover,the following conditions lacuna!:

the ground speed of the aircraft is less than or equal to apredetermined threshold (ground speed less than or equal to the maximumspeed allowed in the course of the approach procedure),

the altitude of the aircraft above the ground is less than or equal to apredetermined threshold (altitude less than or equal to the maximumdecision altitude in the course of the approach procedure),

the aircraft is at least substantially in the axis of the runway (with acertain latitude on either side of the axis so as to take account of anytype of approach along this axis),

the aerodynamic configuration of the aircraft corresponds to the landingphase thereof (slats and flaps extended, gear lowered).

As can be seen in FIG. 1, these various information items are sent tothe inputs of an AND gate 16, namely:

positive comparison via the link 17,

aircraft speed via the link 18,

aircraft altitude via the link 19,

aircraft heading via the link 20,

aerodynamic configuration of the aircraft via the link 21,

configuration of the landing gear via the link 22.

With all these conditions fulfilled simultaneously, the alert or alarmis inhibited (link 23 between the output of the AND gate 16 and thealert or alarm means 7). This means, for the pilot, an absence of visualand audible alarm information. Inhibition of the alarm thus occurs sometime in advance, equal at most to the extrapolation time chosen for thetrajectory, for example 30 seconds as already indicated.

It should moreover be noted that, in the vicinity of the runway, thedefinition of the grid of geographic coordinates of the terrain becomesfundamental. In other words, it is then necessary to have a sufficientlyfine meshing in the immediate area around the runway so as to enhanceprecision in order unambiguously to determine whether the runway isactually being aimed at.

I claim:
 1. A method for supplying information, an alert or an alarm foran aircraft manoeuvering above terrain with known relief, when atrajectory of the aircraft is capable of intercepting the relief of saidterrain, the method comprising:(a) establishing for said terrain a gridof geographic coordinates comprising a plurality of meshes, each of theplurality of meshes having associated therewith a defined portion of therelief; (b) predicting the trajectory of the aircraft over apredetermined time interval; (c) determining whether an intersectionexists between said trajectory and the portion of the relief associatedwith at least one of said meshes; (d) triggering the alert or alarm inaccordance with a result of step (c); (e) performing a comparisonbetween (i) the meshes of the grid having portions of the relief whichare determined in step (c) to have intersections with said predictedtrajectory and (ii) the meshes containing portions of a runway for theaircraft to determine whether any of the meshes having the portions ofthe relief which are determined in step (c) to have intersections withthe predicted trajectory also contains a portion of the runway, so that,if said comparison determines that none of the meshes having theportions of the relief also contains a portion of the runway, the alertor alarm remains capable of being activated, whereas the alert or alarmis inhibited if said comparison determines that at least one of themeshes having the portions of the relief also contains a portion of therunway and the following conditions are simultaneously fulfilled:aground speed of the aircraft is less than or equal to a predeterminedthreshold ground speed; an altitude of the aircraft above the ground isless than or equal to a predetermined threshold altitude; the aircraftis at least substantially in an axis of the runway; and an aerodynamicconfiguration of the aircraft corresponds to a landing phase of theaircraft.
 2. The method as claimed in claim 1, wherein step (a)comprises establishing a first plurality of meshes in a vicinity of therunway and a second plurality of meshes outside the vicinity of therunway, the meshes of the first plurality of meshes being smaller thanthe meshes of the second plurality of meshes.
 3. The method as claimedin claim 1, wherein the aerodynamic configuration of the aircraftcomprise a state of extension of slats and flaps of the aircraft and astate of lowering of landing gear of the aircraft.
 4. A device forsupplying information, an alert or an alarm for an aircraft manoeuveringabove terrain with known relief when a trajectory of the aircraft iscapable of intercepting a relief of said terrain, the devicecomprising:grid establishing means for establishing a grid of geographiccoordinates comprising a plurality of meshes for said terrain, each ofsaid plurality of meshes having associated therewith a defined portionof the relief; trajectory predicting means for predicting the trajectoryof the aircraft over a predetermined time interval; intersectiondetermining means for determining whether an intersection exists betweensaid predicted trajectory and the portion of the relief associated withat least one of said meshes; alert or alarm means for outputting thealert or alarm in accordance with a determination made by saiddetermination means; and comparison means for making a comparisonbetween (i) the meshes of said grid having portions of the relief whichare determined by the intersection determining means to haveintersections with said predicted trajectory and (ii) the meshescontaining portions of a runway for the aircraft to determine, and toprovide an output indicating, whether any of the meshes having theportions of the relief which are determined by the intersectiondetermining means to have intersections with the predicted trajectoryalso contains a portion of the runway, such that, if said comparisonmeans determines that none of the meshes having the portions of therelief also contains a portion of the runway, said alert or alarm meansremain capable of being activated, whereas said alert or alarm means areinhibited if said comparison means determines that at least one of themeshes having the portions of the relief also contains a portion of therunway and the following conditions are simultaneously fulfilled:aground speed of the aircraft is less than or equal to a predeterminedthreshold ground speed; an altitude of the aircraft above the ground isless than or equal to a predetermined threshold altitude; the aircraftis at least substantially in an axis of the runway; and an aerodynamicconfiguration of the aircraft corresponds to a landing phase of theaircraft.
 5. The device as claimed in claim 4, further comprising alogic element between said comparison means and said alert or alarmmeans, the logic element having inputs which receive the output suppliedby said comparison means and signals representing said conditions, andthe logic element also having an output which is linked to said alert oralarm means.
 6. The method as claimed in claim 2, wherein theaerodynamic configuration of the aircraft comprises a state of extensionof slats and flaps of the aircraft and a state of lowering of landinggear of the aircraft.
 7. The device as claimed in claim 4, wherein thegrid establishing means comprises means for establishing a firstplurality of meshes in a vicinity of the runway and a second pluralityof meshes outside the vicinity of the runway, the meshes of the firstplurality of meshes being smaller than the meshes of the secondplurality of meshes.
 8. The device as claimed in claim 4, wherein theaerodynamic configuration of the aircraft comprises a state of extensionof slats and flaps of the aircraft and a state of lowering of landinggear of the aircraft.
 9. The device as claimed in claim 7, wherein theaerodynamic configuration of the aircraft comprises a state of extensionof slats and flaps of the aircraft and a state of lowering of landinggear of the aircraft.
 10. The device as claimed in claim 7, furthercomprising a logic element between said comparison means and said alertor alarm means, the logic element having inputs which receive the outputsupplied by said comparison means and signals representing saidconditions, and the logic element also having an output which is linkedto said alert or alarm means.
 11. The device as claimed in claim 8,further comprising a logic element between said comparison means andsaid alert or alarm means, the logic element having inputs which receivethe output supplied by said comparison means and signals representingsaid conditions, and the logic element also having an output which islinked to said alert or alarm means.
 12. The device as claimed in claim9, further comprising a logic element between said comparison means andsaid alert or alarm means, the logic element having inputs which receivethe output supplied by said comparison means and signals representingsaid conditions, and the logic element also having an output which islinked to said alert or alarm means.
 13. The device as claimed in claim5, wherein the logic element comprises an AND gate.
 14. The device asclaimed in claim 10, wherein the logic element comprises an AND gate.15. The device as claimed in claim 11, wherein the logic elementcomprises an AND gate.
 16. The device as claimed in claim 12, whereinthe logic element comprises an AND gate.